The invention relates to a packing sleeve having an outer lateral surface for a printing unit cylinder of an offset printing press.
In a printing press, the circumferential length of the printing plate cylinder is a basically limiting parameter for the format or the printing length of products to be produced. In order to achieve flexibility and variability, it is desirable to overcome this limitation to permit a variation in print length or a variation in format. For general geometrical reasons, it is known that the circumferential length of a cylinder, here the printing plate cylinder or rather the transfer cylinder, is proportional to its radius. To vary the circumferential length of a fixed-radius cylinder in a printing press, on which cylinder a printing plate is receivable, sleeve-form packings (packing sleeves) of different thickness can advantageously be mounted on the cylinder. Such sleeves can in specific constructions be seamless or slit. In other words, packing sleeves can be closed tubes or bodies comprising plate-form objects, which have been bent so that remote extreme edges lie opposite one another. With the sleeve mounted, and with a consequently larger radius, the potential or maximum achievable print length is then greater or longer than without the mounted sleeve. The circumferential length of a transfer cylinder or rubber blanket cylinder needed for an offset printing process can also be varied correspondingly. An enlargement of the effective outer diameter of the cylinder, that is, the circumferential length effective in printing mode, can therefore be achieved.
It is known, for example, from the document U.S. Pat. No. 5,813,336, to mount sleeve-form saddles on printing unit cylinders in a printing press, especially printing plate cylinders and transfer cylinders. Plate-form printing plates can be fixed to sleeve-form saddles. In their outer lateral surface the described sleeve-form saddles have an opening that runs substantially parallel to the figure axis, especially the axis of rotational symmetry of the saddle. The leading edge and trailing edges of a printing plate to be received can be inserted in the opening and be fixed with a printing plate fixing means, not specified in detail. Sleeve-form saddles are provided in different thicknesses (having different outer diameters).
Such packing sleeves have to have a good dimensional stability, for example, they must be able to withstand a compression as a result of cylinders rolling on one another, that is, a force acting in the radial direction. On the other hand, they must be resilient in the peripheral direction (circumferential direction), if a printing plate or a rubber blanket to be received on the outer lateral surface is to be tensioned. At the same time, the surface regions that absorb the tension forces should withstand the pressure generated, so that a comparatively rigid, stiff or low-resilience material is preferred for this in order to avoid wear.